RELAXATION OF PORE PRESSURE IN A SLENDER CORE OF A ROCKFILL DAM

The relaxation of pore pressure in the core of a rockfill dam, that is caused by a rapid discharge of the water from the reservoir, is contr olled by two different time scales. The time scale due to de-consolida tion is irrelevant, whereas the time scale due to the displacement rat e of the phreatic surface is equal to the ratio between the conductivi ty and the porosity. If the core is vertical and slender, the motion o f the phreatic surface is governed by an ordinary first order differen tial equation. If the discharge is instantaneous, the equation is sepa rable and has been solved. Experiments with a Hele Shaw cell show that the agreement between theory and experiment is not too good. The expl anation is that the discharge of liquid from the reservoir in the Hele Shaw cell is not effectively instantaneous. The practical result impl ies that the relaxation time is approximately 1 year for a core of a r eal dam composed of soil whose height and width are 50 and 4 meters, r espectively.